Note 8 - Preferred Stock and Warrants (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended		12 Months Ended
	Jun. 05, 2018	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			500,000
Payments for Repurchase of Warrants	$ 3,200		$ 3,175
Warrants and Rights Outstanding			$ 0
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 8.40
Series A Preferred Stock [Member]
Stock Redeemed or Called During Period, Shares		9,360			8,661	9,979
Preferred Stock, Redemption Price Per Share			$ 1,000		$ 1,000	$ 1,000
Preferred Stock, Shares Outstanding, Ending Balance			0